It goes mouldy.
Then you throw it away.
This depends on temperature and humidity of your area. Left in the bread box wrapped in plastic about 3 to 5 days. Refrigerated about 7 to 10 days and frozen, several weeks.
Toasted bread does not spoil! it molds!
I find bread goes mouldy in about a week if left in its plastic bag - but that's in an English climate.
it takes 7 days if left out
Seven.
A bread box is a small, enclosed space. In the days before plastic bags and plastic wrap, that small space would become more humid from the bread in it and the enclosure would reduce the rate at which the humidity was diffused. Thus, the bread in the bread box would not dry out as quickly as it would if left on the cupboard shelf. Dried bread is stale bread and is not fresh.
Bread will get moldy whether bagged or not. If moist bread is contained in a plastic bag, the moisture would promote mold growth. Bread left open in a dry room would lose moisture, creating a dryer surface that would slow mold growth.
Around seven or eight days.
I have some left over bread.
There are seven days in a week so: 71 days / 7 days/week = 10 weeks and 1 day left over.
Since there are seven days per week, then simply divide the number of days by seven. Any remainder in your problem would be days left over, or a partial week. 165 / 7 = 23 weeks and 4 days
Mould will grow faster in a plastic bag if it's not kept refrigerated. If it's left in a paper bag, it will firstly go crusty, then mouldy but the plastic bag option will make it go mouldy faster because of the condensation which is produced. I work in a bakery.